Environmental Engineering Reference
In-Depth Information
fulvic molecule; and (iii) has hydroxyl and carbonyl groups that, put together,
are as abundant as carboxyl groups (5-7 mmol g
−
1
). Therefore, an average ful-
vic acid molecule (molecular weight 2,000 g mol
−
1
) would have one carboxylic,
hydroxyl or carbonyl group every three carbon atoms. Amino acids, amino sug-
ars, ammonium (NH
4
+
) and nucleic acid bases make up 45-59 % of fulvic acid-N
(Smith and Epstein
1971
).
The stable carbon isotope (
δ
13
C
=
13
C/
12
C) fractionation of standard SRFA is
-27.6 ‰, while other isolated allochthonous fulvic acids in rivers have [-(25.6-
26.4 ‰)] and in lakes have [
−
(23.02-33.13) ‰]. These data indicate that SRFA
are most likely derived from higher plant matter (Thurman
1985a
; McIntyre et al.
2005
; Senesi
1990
; Simpson et al.
2002
; Caraco et al.
1998
). Note that standard
FAs of Elliot Soil I have
δ
13
C
=
−
25.4 ‰, Elliot Soil II have
δ
13
C
=
−
25.6 ‰,
Pahikee peat I have
δ
13
C
=
−
25.8 ‰. Reference FA of Suwannee River have
δ
13
C
=
−
27.9 ‰, Pahikee peat I have
δ
13
C
=
−
26.1 ‰, Nordic Lake have
δ
13
C
=
−
27.8 ‰ (Senesi
1990
).
Terrestrial DOM from groundwater, streams, rivers, lakes and sea water
(0 salinity) is confined to a narrow range of
δ
13
C (from -25.3 ‰ to -28.6 ‰),
with 80 % of the values falling within 0.5 ‰ of -27.0 ‰ (Schiff et al.
1997
;
McCallister et al.
2004
; McIntyre et al.
2005
; Elder et al.
2000
; Nagao et al.
2011
; Fry and Sherr
1984
). Note that the
δ
13
C is largely different for fresh
deciduous leaves (-30.4 ‰), it increases in the top soil (-28.9 ‰) and then
from -27.8 to -26.4 ‰ in soil. Plant leaves with C3 photosynthesis have
δ
13
C
=
-(25.9-29.2 ‰) and soil profiles have
δ
13
C
=
-(23.8-25.9 ‰).
δ
13
C
has lower values in litter-rich soil DOC [
−
(26.6-27.7 ‰)] than in litter-lack-
ing soil DOC [approximately
−
(23-27 ‰)] or terrigenous soil with surface/
forest litter [
−
(23-27 ‰)], terrestrial leaf OM (
−
27 ‰), terrigenous vascular
plant [
−
(26-30 ‰)], yellow soil profile [
−
(21.1-24.8 ‰)] or limestone soil
profile [
−
(23.0-24.1 ‰)] (Tu et al.
2011
; McCallister et al.
2004
; Elder
et al.
2000
; Trumbore et al.
1992
; Deegan and Garritt
1997
; Stevenson
1982
;
Richter et al.
1999
; Raymond and Bauer
2001b
; Cloern et al.
2002
; Zhu and
Liu
2006
; Stenson et al.
2002
). Therefore, the origin of allochthonous DOM is
significantly dependent on the types and nature of terrestrial vegetation in soil
environments.
The combination of flow path analysis and
14
C content of DOC suggests that
the DOC in upland streams is composed of two pools (Schiff et al.
1997
). First,
the DOC pool is carried to the stream by discharging groundwater. This DOC
has been extensively recycled in the soil zone, has low
14
C content and proba-
bly has a low proportion of labile functional groups. Although groundwater con-
tributions to stream flow are high even during storm events, groundwater DOC
concentrations are low. The relative contribution of this older recalcitrant pool
is limited by the amount of soluble carbon which elutes through the overlying
soil column. The second pool is composed of recently fixed and potentially more
microbially labile DOC leached from the A horizon or litter layer. The potential
contribution of this second pool is very high especially after leaffall.
